SIMS analysis of zinc oxide LED structures: quantification and analysis issues

Zinc oxide (ZnO) is a wide band gap semiconductor that shows great promise for development of light emitting diode structures. Interest in this technology has increased significantly, but even though controlled n-type doping can be readily achieved, p-type doping has been difficult. Numerous potential p-type dopants were investigated in this SIMS study using a CAMECA IMS-6F. The dopants and other elements of interest were quantified by use of ion implantation into ZnO substrates. Relative sensitivity factor values were obtained for H, Li, N, F, Na, Mg, Al, Si, K, Ga, As, Se, Ag, Cd, Te. Sample charging was encountered for some specimens, and adjacent electron neutralization procedures were employed. ZnO structures were prepared and subsequently analyzed with both O2+ and Cs+ primary beams. Depth profiles exposed a number of analysis issues. Because of the large number of elements, especially those at low atomic number, that were present in the structures, many mass interferences were encountered. Ag in particular was very difficult to monitor. Matrix effects were also noted, especially when high Mg doping was used. The need to monitor Al, Na, and K in the near surface region required analysis without conductive Au coating to reduce contamination. With careful choice of secondary ion species, it was possible to monitor the elements of primary interest using O2+ primary beam. SIMS demonstrated the ability to characterize the layers in the ZnO structure, including quantum wells, and to determine dopant and contaminant levels. Copyright © 2012 John Wiley & Sons, Ltd.